If  there is a requirement where you want to create multiple shipping categories in Oscommerce that a user can select like

No Shipping :  $0.00
Flat Rate Manhattan: $25.00
Flat Rate Overnight Manhattan: $30.00

Then just follow the steps given below:

Create copy of “flat.php” Ex: flat2.php,flat3.php in

catalog\includes\modules\shipping and
catalog\includes\languages\english\modules\shipping.

Open catalog\includes\languages\english\modules\shipping\flat2.php and replace lines with the following.

define(‘MODULE_SHIPPING_FLAT2_TEXT_TITLE’, ‘Flat Rate 2’);
define(‘MODULE_SHIPPING_FLAT2_TEXT_DESCRIPTION’, ‘Flat Rate 2’);
define(‘MODULE_SHIPPING_FLAT2_TEXT_WAY’, ‘Best Way 2’);

Open catalog\includes\modules\shipping\flat2.php  replace term flat with flat2 and MODULE_SHIPPING_FLAT with MODULE_SHIPPING_FLAT2.

Thats it..now upload to respective  Southfayettenursing roulette directory. Go to Admin section and enable new shipping modules.